NSTX-Upgrade

Title:Control of Neutral Fueling and Helium Exhaust in NSTX-Upgrade Plasmas by Three-Dimensional Magnetic Control Fields.

Short description (public abstract):

This research targets the understanding and optimization of the physical processes that define fueling and exhaust of high temperature plasmas, which are being explored as a means to accomplish energy production by nuclear fusion. Very much like in a combustion engine, a well-controlled amount of fueling and efficient exhaust has to be realized to keep the burn media clean and at desired pressures for sustained energy production. In fusion plasma, hydrogen isotopes represent the fuel while helium is the ash (the “fusion product”) from the reaction cycle. Hydrogen is supplied from the outside into the outer boundary of the plasma. In contrast, the helium is born predominantly inside of the plasma. Hence, an efficient control mechanism for fueling and exhaust also deals with desired inward transport of fuel and outward transport of helium and impurities.

Three-dimensional magnetic fields have been used as an innovative control tool for plasma edge transport and for dedicated interaction with the neutral particle source at the surrounding wall elements. They will be employed in this research to address neutral fueling, as a particularly important topic in the spherical tokamak (ST) NSTX-Upgrade. The ST magnetic confinement concept offers more stable, high performance plasma operation at reduced system size. It therefore is an attractive candidate for compact fusion energy development facilities. However, the concept so far suffers from weak plasma density control, which limits the plasma regimes accomplished as well as the duration of an experiment pulse. This research aims on exploring if dedicated density control including reduction of impurity contamination of the plasma and sufficient helium exhaust can be accomplished by use of three-dimensional magnetic control fields. The work encompasses development and validation of suitable numerical tools to gain predictive capability for future devices and reactor scale experiments.